Cosplayer Johnny McPhung as Robin poses at Day 2 of WonderCon 2023 at Anaheim Convention Center on March 25, 2023 in Anaheim, California. (Photo by Daniel Knighton/FilmMagic)
A drone view shows vehicles in the area affected by the floods, in Encantado, Rio Grande do Sul state, Brazil, on May 3, 2024. (Photo by Diego Vara/Reuters)
A Pure Green Sweat Bee (Augochlora pura) covers itself in pollen while pollinating the flower of a squash plant in Toronto, Ontario, Canada, on August 23, 2024. (Photo by Creative Touch Imaging Ltd/NurPhoto/Rex Features/Shutterstock)
A blue crab, a highly invasive alien species, is seen at Lio Piccolo during the reforestation day on April 05, 2025 in Venice, Italy. The island of Lio Piccolo in the northern lagoon of Venice is being replanted with 16,000 new trees that will protect the salt marsh ecosystem that is fundamental to the natural health of Venice and the lagoon by WOWnature project, an Etifor initiative. (Photo by Simone Padovani/Getty Images)
In animals, yawning can serve as a warning signal. For example, Charles Darwin, in his book The Expression of the Emotions in Man and Animals, mentioned that baboons yawn to threaten their enemies, possibly by displaying large canine teeth. Similarly, Siamese fighting fish yawn only when they see a conspecific (same species) or their own mirror-image, and their yawn often accompanies aggressive attack. Guinea pigs also yawn in a display of dominance or anger, displaying their impressive incisor teeth. This is often accompanied by teeth chattering, purring and scent marking.
A man sits under lanterns and decorations on a street ahead of the Chinese Lunar New Year in Chinatown Yangon, Myanmar January 23, 2017. (Photo by Soe Zeya Tun/Reuters)